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Full text of "Text Book Of Mechanical Engineering"

446

Cuhnanris Theorem.

Project ST from L, uv from c, w x from M, YZ from N, and
ab from B, and the curve of Shearing Force is obtained, measure-
able by load scale. Also s# —Rt and Tv = Rt2 (See pp. 855
and 1085.)

A Parabola may be drawn by the method in Fig. 405,
which consists in dividing A B and B o into an equal number of
parts, and joining the divisions of A B to D by lines cutting the
divisions of B c, then tracing the curve through the crossing
points.

We will now take some examples to illustrate the equation of
Bmto/Z. The shear diagram is not often required in practice,
but should at least be made for trial in short beams.

Example 22.—The following beams are proposed for a central load
and given span : (i) a bar 4" deep by 2" wide ; (2) a bar 3*8" dia. ;
(3) a bar 3-5" square. What are their relative strengths ? (Eng.
Exam. 1885.)

Br^/Z   or — =/2        /. W oc Z

(2)
(3)

4

2 x i6

~~6~

_22x 3*3 x 3*8 x'jS _

5.:33_

: 5'388    a roi

^ -    £L>L3J2i3^    __„.
"6                   6             ~

7*14.5    a 1-34